Neisseria meningitidis is a major cause of death and morbidity throughout the world. Neisseria meningitidis causes both endemic and epidemic diseases, principally meningitis and meningococcemia [Gold, Evolution of meningococcal disease, p. 69, Vedros N. A., CRC Press (1987); Schwartz et al., Clin. Microbiol. Rev., 2, p. S118 (1989)]. In fact, this organism is one of the most common causes, after Haemophilus influenza type b, of bacterial meningitis in the United States, accounting for approximately 20% of all cases. It has been well documented that serum bactericidal activity is the major defense mechanism against Neisseria meningitidis and that protection against invasion by the bacteria correlates with the presence in the serum of anti-meningococcal antibodies [Goldschneider et al., J. Exp. Med. 129, p. 1307 (1969); Goldschneider et al., J. Exp. Med., 129, p. 1327 (1969)].
Neisseria meningitidis are subdivided into serological groups according to the presence of capsular antigens. Currently, 12 serogroups are recognized, but serogroups A, B, C, Y, and W-135 are most commonly found. Within serogroups, serotypes, subtypes and immunotypes can be identified on outer membrane proteins and lipopolysaccharide [Frasch et al., Rev. Infect. Dis. 7, p. 504 (1985)].
The capsular polysaccharide vaccines presently available are not effective against all Neisseria meningitidis isolates and do not effectively induce the production of protective antibodies in young infants [Frasch, Clin. Microbiol. Rev. 2, p. S134 (1989); Reingold et al., Lancet, p. 114 (1985); Zollinger, in Woodrow and Levine, New generation vaccines, p. 325, Marcel Dekker Inc. N.Y. (1990)]. The capsular polysaccharide of serogroups A, C, Y and W-135 are presently used in vaccines against this organism. These polysaccharide vaccines are effective in the short term, however the vaccinated subjects do not develop an immunological memory, so they must be revaccinated within a three-year period to maintain their level of resistance.
Furthermore, these polysaccharide vaccines do not induce sufficient levels of bactericidal antibodies to obtain the desired protection in children under two years of age, who are the principal victims of this disease. No effective vaccine against serogroup B isolates is presently available even though these organisms are one of the primary causes of meningococcal diseases in developed countries. Indeed, the serogroup B polysaccharide is not a good immunogen, inducing only a poor response of IgM of low specificity which is not protective [Gotschlich et al., J. Exp. Med., p. 129, 1349 (1969); Skevakis et al., J. Infect. Dis., 149, p. 387 (1984); Zollinger et al., J. Clin. Invest., 63, p. 836 (1979)]. Furthermore, the presence of closely similar, crossreactive structures in the glycoproteins of neonatal human brain tissue [Finne et al., Lancet, p. 355 (1983)] might discourage attempts at improving the immunogenicity of serogroup B polysaccharide.
To obtain a more effective vaccine, other Neisseria meningitidis surface antigens such as lipopolysaccharide, pili proteins and proteins present in the outer membrane are under investigation. The presence of a human immune response and bactericidal antibodies against certain of these proteinaceous surface antigens in the sera of immunized volunteers and convalescent patients was demonstrated [Mandrell and Zollinger, Infect. Immun., 57, p. 1590 (1989); Poolman et al., Infect. Immun., 40, p. 398 (1983); Rosenquist et al., J. Clin. Microbiol., 26, p. 1543 (1988); Wedege and Froholm, Infect. Immun. 51, p. 571 (1986); Wedege and Michaelsen, J. Clin. Microbiol., 25, p. 1349 (1987)].
Furthermore, monoclonal antibodies directed against outer membrane proteins, such as class 1, 2/3 and 5, were also reported to be bactericidal and to protect against experimental infections in animals [Brodeur et al., Infec. Immun., 50, p. 510 (1985); Frasch et al. Clin. Invest. Med., 9, p. 101 (1986); Saukkonen et al. Microb. Pathogen., 3, p. 261 (1987); Saukkonen et al., Vaccine, 7, p. 325 (1989)].
Antigen preparations based on Neisseria meningitidis outer membrane proteins have demonstrated immunogenic effects in animals and in humans and some of them have been tested in clinical trials (Bjune et al., Lancet, p. 1093 (1991); Costa et al., NIPH Annals, 14, p. 215 (1991); Frasch et al., Med Trop., 43, p. 177 (1982); Frasch et al., Eur. J. Clin. Microbiol., 4, p. 533 (1985); Frasch et al. in Robbins, Bacterial Vaccines, p. 262, Praeger Publications, N.Y. (1987); Frasch et al, J. Infect. Dis., 158, p. 710 (1988); Moreno et al. Infec. Immun., 47, p. 527 (1985); Rosenqvist et al., J. Clin. Microbiol., 26, p. 1543 (1988); Sierra et al., NIPH Annals, 14, p. 195 (1991); Wedege and Froholm, Infec. Immun. 51, p. 571 (1986); Wedege and Michaelsen, J. Clin. Microbiol., 25, p. 1349 (1987); Zollinger et al., J. Clin. Invest., 63, p. 836 (1979); Zollinger et al., NIPH Annals, 14, p. 211 (1991)]. However, the existence of great interstrain antigenic variability in the outer membrane proteins can limit their use in vaccines (Frasch, Clin. Microb., Rev. 2, p. S134 (1989)]. Indeed, most of these preparations induced bactericidal antibodies that were restricted to the same or related serotype from which the antigen was extracted [Zollinger in Woodrow and Levine, New Generation Vaccines, p. 325, Marcel Dekker Inc. N.Y. (1990)]. Furthermore, the protection conferred by these vaccines in young children has yet to be clearly established. The highly conserved Neisseria meningitidis outer membrane proteins such as the class 4 [Munkley et al. Microb. Pathogen., 11, p. 447 (1991)] and the lip protein (also called H.8) [Woods et al., Infect. Immun., 55, p. 1927 (1987)] are not interesting vaccine candidates since they do not elicit the production of bactericidal antibodies. To improve these vaccine preparations, there is a need for highly conserved proteins that would be present at the surface of all Neisseria meningitidis strains and that would be capable of eliciting bactericidal antibodies in order to develop a broad spectrum vaccine.
The current laboratory diagnosis of Neisseria meningitidis is usually done by techniques such as Gram stain of smear preparations, latex agglutination or coagglutination, and the culture and isolation on enriched and selective media [Morello et al., in Balows, Manual of Clinical Microbiology, p. 258, American Society for Microbiology, Washington (1991)]. Carbohydrate degradation tests are usually performed to confirm the identification of Neisseria meningitidis isolates. Most of the described procedures are time-consuming processes requiring trained personnel. Commercial agglutination or coagglutination kits containing polyvalent sera directed against the capsular antigens expressed by the most prevalent serogroups are used for the rapid identification of Neisseria meningitidis. However, these polyvalent sera often nonspecifically cross-react with other bacterial species and for that reason should always be used in conjunction with Gram stain and culture. Accordingly, there is a need for efficient alternatives to these diagnostic assays that will improve the rapidity and reliability of the diagnosis.